Compressor unloading system



June 2, 1959 J. LE VALLEY 2,889,106

COMPRESSOR UNLOADING SYSTEM Filed March 28, 1955 2 Sheets-Sheet l INVENTOR JOHN LE VALLEY Fla 2 June 2, 1959 J. LE VALLEY COMPRESSOR UNLOADING SYSTEM Filed March 28, 1955 so 89 e2 "w l ((5%? L. LL9

2 Sheets-Sheet 2 INVENTOR JOHN LE VALLEY HIS ATTORNEY United States Patent COMPRESSGR UNLOADING SYSTEM John Le Valley, Painted Post, N .Y., assignor to Ingersoll- Rand Company, New York, N.Y., a corporation of New Jersey Application March 28, 1955, Serial No. 497,071

8 Claims. (Cl. 230-2) This invention relates to gas compressor systems, and more particularly to an improved unloading system for compressors of two or more compression stages.

One object of the invention is to provide an unloading system for a motor driven compressor having a direct driven lubricating pump which insures quick priming of the pump after the compressor has started.

Another object is to provide unloading means for a compressor having a discharge gas receiver which will bleed the pressure gas from the receiver whenever the compressor is shut down, in order to avoid accumulation of water in the system due to condensation from the gas in the receiver.

A further object is to provide a simple and reliable unloading arrangement for such a compressor which isolates the compressor from the main discharge line whenever the compressor is shut down and which will be economical and easily maintained.

Other objects and the advantages thereof will be in part obvious and in part pointed out in the following description and the accompanying drawings which illustrate a preferred embodiment of the invention in which similar numerals refer to similar parts, and in which Fig. 1 is a side elevation, partly in section, of a twostage compressor unloading system constructed in accordance with the practice of the invention,

Fig. 2 is a side elevation, partly in section, of the compressor, showing more particularly the lubricating and cooling features of the compressor,

Fig. 3 is a longitudinal section of a check valve, and

Fig. 4 is a section through a bleeder valve mounted on the side of the check valve as indicated in Fig. 3.

Referring to the drawings, the invention is shown as applied to a two-stage compressor unit 20 of a system which, in this case, supplies gas under pressure to a header 22 for distribution to or connection with other compressors. A check valve 24 is provided to isolate the compressor unit 28 from the header 22. The compressor unit 20 comprises a two-stage compressor 26, preferably of the well-known rotary or vane type having a gear pump 28 to supply oil for cooling and lubricating the compressor and which is driven by a motor 30 through the compressor shaft 31. Gas from a supply source (not shown) enters the compressor 26 through a conduit 32 and an inlet valve 34 and is discharged under pressure through a discharge valve 36 and a conduit 38 into a receiver 40 and thence through the check valve 24 and a conduit 42 into the header 22. The pump 28 draws oil from the bottom of the receiver 40, acting as a sump, through a pipe 44 and forces it to the compressor first and second stage compartments. Here the oil is picked up by the gas being compressed and carried back to the receiver 40 where it separates from the gas and settles to the bottom thereof.

The check valve 24 is adapted to complete communication between the receiver 40 and the conduit 42 in response to a predetermined pressure difierential between the compressor discharge gas pressure and the compressor 2,889,106 Patented June 2, 1959 interstage gas pressure to assure a rapid build-up of discharge pressure in the receiver 40 to prime the pump 28 soon after the compressor has started. When. the compressor 26 has stopped, the valve 24 is adapted to cut off communication between the receiver 40 and the conduit 42 in response to an equalization of the discharge and interstage gas pressures. Finally, the valve 24 includes means for bleeding the pressure gas from the receiver after the motor 30 has stopped in response to a drop in motor oil pressure.

Referring in greater detail to the construction of the compressor unit 20, the compressor 26, shown in Fig. 2, is lubricated and cooled by oil supplied by the gear pump 28. For this purpose the pump 28, which is of conventional design, includes a gear 45 keyed to the compressor shaft 31 and meshing with a gear 46 rotatable on a stationary shaft 47, all mounted Within the casing 48 of the compressor 26. The casing 48 is provided with a passage 49 for conducting oil from the pump discharge chamber 58 through a jet 51 into the first stage compartment 52, and a passage 54 for conducting oil from the chamber 50 through a jet 56 into the second stage compartment 58.

The inlet valve 34 is adapted to admit gas from the intake conduit 32 to the compressor 26, at the same time preventing reverse flow of such gas. To this end the valve 34, which is of typical check valve construction, includes a valve 68 normally held in the closed position by a spring 62.

The discharge valve 36 is similarly adapted to permit the flow of pressure gas in only one direction from the compressor 26 into the discharge conduit 38 and is likewise of check valve construction including a valve 64 resiliently seated by a spring 66.

Upon leaving the compressor 26 the gas, which has picked up oil therein, passes through the conduit 38 into the receiver 40 which confines the oil-laden gas and is provided with means to separate the oil from the gas. Accordingly, the receiver 40, which is similar to the receiver shown in my copending application Serial No. 183,421, filed September 6, 1950, now abandoned, contains a separator 67 to remove the oil from the gas and collects the oil at the bottom to serve as an oil sump for the gear pump 28.

In accordance with the practice of the invention, the check valve 24 controls the flow of pressure gas from the receiver 40 to the header 22. For this purpose the valve 24, more clearly shown in Fig. 3, comprises a body 68 threadedly connected to the receiver 48 and the conduit 42 and formed to provide a seat for a poppet type of valve 70. The valve 70 is normally held in the closed position by biasing springs 71 interposed between the valve and a bonnet 72 fastened to the body 68 by screws 73, but may also be closed by a manually rotatable stem 74 threaded in the bonnet 72 and bearing against the outer surface of the valve 7 8. The inner end of the stem 74 is formed to slidably receive an extension 75 of the valve 70 for guiding the valve and also limits the free movement thereof.

The valve 78 is opened after the compressor 26 has started in response to a predetermined pressure differential between the compressor discharge gas pressure and interstage gas pressure. In furtherance to this end the valve 78 is actuated by a diaphragm 76 fixedly attached at its central portion to the stem 78 of the valve which ,3 slidably fits the. body 68. The diaphragm is held in place by a stud 80 passing through the diaphragm and threaded in the stem 78 and by a nut 82 on the stud clamping the diaphragm between a pair ofwashers 84. The outer with the body inner and outer chambers 98 and 92, re-

spectively. The outer chamber 92 is in constant communication with the inlet or receiver side of the check valve 24 by means of a passage 94 formed in the body 68 and the cover 86. The body as is also provided with a passage 96 which, together with an interconnecting conduit 98, connects the inner chamber 9t) with the discharge side of the compressor first stage compartment 52. Thus the diaphragm '76 is exposed to interstage gas pressure in the chamber 90 and to discharge gas pressure in the chamber 92 and is, therefore, adapted to open the valve 70 whenever the differential between these pressures acting on the diaphragm exceeds the force exerted by the springs 71.

Such a condition is permitted to exist only after the pressure of the gas in the receiver has forced oil therein through the pipe 44 to the gear pump 28 to insure priming thereof soon after the compressor has started. This is brought about in the following manner. After the compressor is started the interstage gas pressure in the chamber 90 quickly rises to a maximum, say of thirty pounds, and. acting upon the diaphragm 76 supplements the force of the springs 71 to hold the valve 70 in the closed position. The pressure of the discharge gas in the chamber 92 and in the relatively large volume receiver 40, on the other hand, requires a longer time to build up but soon exceeds the interstagc pressure acting on the discharge side of the pump 28 to force oil to the pump for lubricating the compressor. When the discharge gas pressure reaches, for example, forty or fifty pounds, depending upon the opposing force of the springs 71 selected to predetermine such force, the pressure differential acting on the diaphragm 76 is sufficient to open the valve 70 to admit discharge gas in the receiver 40 through the conduit 42 into the header 22 where it may be combined with pressure gas from other compressors.

In order to prevent reverse flow of gas from the header 22 to the receiver 4t), the valve 70 is closed by the diaphragm '76 soon after the compressor 26 has stopped, thereby isolating the compressor from the header during a period of compressor shut down. This occurs whenever the pressure difierential acting on the diaphragm drops below the force of the springs 71, or in other words, only when the discharge pressure in the chamber 92 approaches in value the interstage pressure in the chamber 0. To this end the receiver 40 is connected to the discharge side of the compressor second stage compartment 58 by a conduit 100 of relatively small capacity which serves to by-pass the discharge valve 36. In order to prevent the flow of gas through the conduit h from the compressor to the receiver 4% during operation of the compressor and permit reverse flow when the compressor is shut down, a check valve 102 of relatively restricted capacity in comparison to the capacity of the discharge conduit 38 is provided in the conduit 100. Thus when the compressor 26 stops, the pressure of the discharge gas in the receiver 40 closes the discharge valve 36 and opens the check valve 102 and forces a small amount of gas through the conduit 100 into the second stage compartment 58, whence it leaks past the compressor rotor into the first stage compartment 52 and out through the conduit $3 into the chamber 90. Accordingly, since the compressor volume is small the pressures of the gas in the chambers 90 and 92 are rapidly equalized and the pressure differential therebetween dissipated, thereby permitting the springs 71 to close the valve 70. The valve 70 will remain closed until the compressor 26 is re-started to close the check valve 102 and repeat the above-described cycle.

After the compressor 26 has stopped and the check valve 24 has closed, the discharge gas in the receiver 40 would normally remain trapped therein. Inasmuch as the receiver 40 cools down, the inherent moisture in the gas would condense and the resulting water would accumulate at the bottom whence it would be drawn into the pump ahead of the oil unless it were drained off.

Since i the disadvantages of such a condition are obvious it is desirable to prevent such an occurrence. For this reason the check valve 2 incorporates a bleeder valve 104 positioned on the receiver side of the valve 70 to control the flow of gas in the receiver at to the atmosphere.

It is also most desirable that when the compressor is restarted, it should be unloaded by bleeding the compressed air out of the system as above described. Otherwise, the equalizing of pressures in the compressor stages would put an abnormal load on the driving motor to make starting difiicult.

It will be understood that the bleeder valve 104 could also be located on the receiver, but is included in the valve 24 for the sake of convenience.

As shown in Fig. 4 the valve 1% comprises a plunger Hi6 slidably fitting in a housing 103 having a discharge port 107 in communication with the receiver and atmosphere. A part of the plunger 106 being adapted to sit in the port 107 prevents the escape of gas from the receiver. The plunger 1% is closed by a diaphragm 110 bearing thereagainst and clamped at its outer peripheral portion between the housing 103 and a cover 112 by screws 1 4. The cover 112 is formed to provide a chamber 116 on the side of the diaphragm 110 opposite the plunger 106 and which is connected with the motor lubricating system by a passage 11% in the cover 112 and a pipe 120 connecting the cover with the motor 30. The lubricating system of the motor 30 can be of any known type in which there is oil under pressure when the motor is operating and no oil under pressure when the motor is stopped. For example, the system can be similar to the compressor lubricating system disclosed herein or similar to the system shown in United States Patent #652,724. Accordingly, the diaphragm 110, in response to motor oil pressure, holds the plunger 106 in the closed position to maintain gas pressure in the receiver 40 so long as the motor is running. However, when the motor 30 stops, the oil pressure in the chamber 116 drops to permit the gas in the receiver to open the plunger 1% to bleed the receiver gas to the atmosphere, thereby unloading the compressor 26 and avoiding the accumulation of water in the receiver due to condensation from the gas.

It will be seen, therefore, that after the compressor stops, the check valve 24 simultaneously blocks the flow of gas from the receiver 40 to the header 22 and by means of the bleeder valve 104 exhausts the residual gas in the receiver to the atmosphere. Consequently, by isolating the compressor unit 20 from the header 22 the valve 24 prevents the escape of gas from the header through the receiver to the atmosphere in order to permit bleeding of the receiver.

Thus a simple and dependable unloading arrangement for a two or more stage compressor system is provided which not only disconnects the compressor from the main discharge line and bleeds the compressor system of pressure gas after the compressor has stopped, but also assures prompt lubrication of the compressor after it has started.

I claim:

1. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a check valve in said receiver outlet, a spring operatively connected to said check Valve urging said valve closed, means operatively connected with the valve and responsiVe to a predetermined diiferential between the compressor discharge and an inter-stage pressure to open the check valve, a conduit restricted in comparison to the discharge conduit connected to the receiver and the discharge side of the last stage of the compressor upstream of said discharge valve, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

2. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a pressure operated check valve in said receiver outlet, an actuating member for the check valve operatively connected thereto and having a surface exposed to the receiver pressure for opening the check valve and a surface opposing the first said surface exposed to an interstage pressure of the compressor, a spring operatively connected to said check valve urging said valve closed, a conduit restricted in comparison to the discharge conduit connected to the receiver and to the discharge side of the last stage of the compressor, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

3. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a pressure operated check valve in said receiver outlet, a flexible member to actuate the check valve operatively connected thereto and including a surface "subjected to the receiver pressure to open said check valve and having a surface opposing the first said surface subjected to a compressor inter-stage pressure tending to close said check valve, a spring operatively connected to the check valve constantly urging said valve into closed position, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

4. A compressor unloading system comprising a multistage compressor having a shaft and inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a pump connected to the compressor shaft and actuated thereby to circulate oil under pressure from the receiver to the compressor to lubricate the latter, a pressure operated check valve operatively connected to the receiver outlet including a valve body therefor having a chamber, a valve member in the receiver outlet and movable in the valve body and adapted to seat thereon, a diaphragm in the chamber connected to the valve body and the valve member and having a surface exposed to the receiver pressure for unseating the valve member and a surface opposing the first surface exposed to a compres sor inter-stage pressure for seating the valve member and a spring operatively connected to the valve member constantly tending to seat said member, a conduit connecting the receiver to the discharge side of the last stage of the compressor, check means in said conduit to permit limited flow in comparison to the flow permitted by the discharge conduit only in the direction toward the compressor and tending to maintain receiver pressure at the compressor discharge, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

5. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a pressureactuated check valve operatively connected to the receiver including a valve body therefor, a valve member inthe receiver outlet movable in the valve body to opened and closed positions, a diaphragm in the valve body and attached to the valve member acting responsiv'ely to the compressor discharge pressure to urge the valve member to the open position and acting responsively to a compressor inter-stage pressure to urge the member into the closed position connected to the valve member constantly tending to seat said member, a conduit connecting the receiver to the discharge side of the last stage of the compressor, check means in said conduit to permit limited flow in comparison to the flow permitted by the discharge conduit only in the direction toward the compressor and tending to maintain receiver pressure at the compressor discharge, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

6. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubrieating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a discharge valve in said discharge conduit to control flow of discharge therethrough, a pressure-actuated check valve operatively connected to the receiver including a valve body therefor, a valve member in the receiver outlet and slidably mounted in the valve body to seat thereon, a spring operatively connected to the valve member constantly tending to seat said member, a diaphragm connected to the valve member and the valve body and forming with said body on one side an inner pressure chamber exposed to a compressor inter-stage pressure and on the other side an outer pressure chamber exposed-to the compressor discharge pressure, said diaphragm acting responsively to a predetermined differential between the compressor discharge and inter-stage pressures toovercome the force of said spring to unseat the valve member, said spring acting responsively to an equalization of said discharge and inter-stage pressures to seat said valve member, a conduit restricted in comparison to the discharge conduit and connecting the receiver to the discharge side of the last stage of the compressor to effect such equalization, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve for communicating the pressure of said lubricating system to last said valve to hold said valve closed.

7; A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running, a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a check valve in said outlet including a spring tending to close said check valve, means operatively connected With the valve and responsive to a predetermined differential between the compressor discharge and an inter-stage pressure to open the check valve, an exhaust valve communicating with the receiver and oper- 4;; ative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve communicating the pressure of said lubricating system to said means to hold said exhaust valve closed.

8. A compressor unloading system comprising a multistage compressor having inlet and discharge openings for the passage of fluid, an inlet valve in said inlet to control the flow of fluid therethrough, a motor connected to the compressor for driving the compressor and having a lubricating system developing pressure when the motor is running a receiver having an inlet and an outlet, a discharge conduit connected between the compressor discharge opening and the receiver inlet to convey discharge therebetween, a flexible member to actuate the check valve operatively connected thereto and including a surface subjected to the receiver pressure to open said check valve and having a surface opposing the first said surface subjected to a compressor inter-stage pressure tending to close said check valve, a spring operatively connected to the check valve constantly urging said valve into closed position, an exhaust valve communicating with the receiver and operative in its open position to exhaust pressure fluid from the receiver, and pressure responsive means operatively connected to said exhaust valve communicating the pressure of said lubricating system to said means to hold said exhaust valve closed.

No references cited. 

